The effects of chronic insulin administration on the metabolism of isolated rat adipose cells were studied. After 2 weeks of treatment, adipose cell size, and basal glucose transport and metabolism are unaltered, but insulin-stimulated glucose transport and metabolism are increased two- to three-fold. Insulin binding is increased 30-50%, but no shift in the insulin dose-response curve for glucose transport or metabolism occurs. Chronic hyperinsulinemia does not alter basal or epinephrine-stimulated lipolysis. These results suggest that chronic hyperinsulinemia increases insulin binding and the capacity of rat adipose cells to transport and metabolize glucose without changing the cells' sensitivity to insulin. The mechanism of increased insulin-stimulated glucose transport in adipocytes from chronically hyper-insulinemic rats was also examined. Adipocytes from insulin-treated rats show a 55% increase in insulin-stimulated glucose transport activity compared to control rats and a corresponding increase in glucose transporters in the plasma membranes. Basal glucose transport activity and glucose transporters in the plasma membranes were not significantly different. Basal and insulin-stimulated glucose transporters in the low-density microsomes were also unchanged. However, total intracellular glucose transporters in the basal state and the net translocation of intracellular glucose transporters to the plasma membranes in response to insulin were increased because of a 39% increase in low-density microsomal protein. Total protein and water space per cell were also increased in insulin-treated, compared to control, rats. These results suggest that chronic hyperinsulinemia in the rat enhances insulin's stimulatory action on glucose transport in adipocytes by increasing the intracellular pool of glucose transporters through a generalized effect on the net synthesis of intracellular protein.